Nonmicrophonic triode



Oct. 30, 1928.

H. M. FREEMAN NONMICROPHONIC TRIODE Filed March 29, 1924 mvsmoa Huber! M. fieeman WITNESSES:

ATTORNEY Patented Oct. 30, 1928.

UNITED STATES PATENT OFFICE.

HUBER! I. FREEMAN, OF EAST PITTSBURGH, PENNSYLVANIA, ASSIGNOB '10 WEST- INGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION 01' PENN- SYIIVANIA.

NON MIOBOPHONIC TRIODE.

Application filed March 29, 1924. Serial No. 702,715.

My invention relates to thermionic discharge devices.

One obj'ect of my invention is to improve the operating characteristics of thermionic a dischar e devices by reducing microphonic noises t erein.

Another object of my invention is to provide a device whereby the filament of a thermionic discharge device is held under tension when cold, and relieved from tension when hot.

Another object of my invention is to provide a filament mounting for a thermionic discharge device which shall take up part,

but not all, of the expansion of the filament when it is heated to its operating temperature.

Another object of my device is to construct a thermionic discharge triode which shall be usable under conditions which produce vibration of the device and its surroundings.

In the prior art of the construction of thermionic discharge devices, especially of devices having three electrodes, it has been customary to mount the filament upon the supports in such manner that the filament is held under tension at all times. Because of this tension, vibration of the device as a whole would set the filament vibrating at a period of its own in a manner similar to that in which a stretched violin string vibrates. This vibration varies the electron stream and produces a very objectionable variation in the space current through the device, which current variation is perceived in connected signal translating apparatus as a r1nging sound, which not infrequently entirely obscures incoming signals which it is desired to receive by the apparatus of which the triode is a part.

My invention provides a construction whereby the filament is not under tension when it is operating.

Other ob]ects and structural details of my invention will be apparent from the followin description when read in connection with t e accompanying drawings, wherein:

The single figure of the accompanying drawing is a sketch of the device of my invention.

In the figure is shown an evacuated contamer 1, preferably made of glass, integral with which is a reentrant portion 2, also of glass, and a press 3. The container 1 is comented, at one end, into a molded composition holder 4 which also carries a plurality of contact-making terminal lugs 6, 7, 8 and 9. Sealed into the press 3 are provided four supporting wires 11, 12, 13 and 14 connected respectively to the terminal lugs 6, 7, 8 and 9.. To the wire 13 is attached an anode 15. To the wire 11 is attached an auxiliary wire 16 to which, in turn, are attached the convolutions of a grid electrode 17. To the Wire 14, in turn, is attached a filament end piece 18, which, in turn, supports a filament 19. To the wire 12 is attached another filament end piece 21 which supports the other end of the filament 19.

Wires 11, 13 and 14 are made of thick, stifi, material designed to limit the vibration of the elements which they support to a minimum. Wire 12 is made of a smaller diameter material in order to have a predetermined amount of elasticity. The end of wire 12 to which is attached the filament holder 21 is bent to a special shape, as shown, in order to make effective use of its elasticity.

In the construction of my device, the filament 19 is attached, preferably by welding, to the filament end pieces 18 and 21. The end piece 21 is then attached to the wire 12, also preferably by welding. A definite amount of pull is then applied by the builder to the end piece 18, whereby the filament 19 is stretched, and a predetermined tension is applied to the elastic portion of the wire 12. The end piece 18 is then attached, preferably by welding, to the wire 14:.

By this construction, a small but definite tension is placed upon the filament 19 when it is cold, through the agency of the springiness of the wire 12. The displacement of the end of wire 12 by this tension is, however, but slight. Upon energizing the triode for operation and heating the filament 19, it expands. The tension upon the filament 19 causes, in the cold, a dis lacement of the end of wire 12. When t e filament 19 is heated to the predetermined temperature, its expansion from heating allows the end of the wire 12 to move back to its unrestrained position. Wire 12, in so doing, takes up nearly, but not quite, all of the expansion of the filament 19. The stiflfness of the wire 12 and the initial tension on the filament are such that the displacement of the end of wire 12 is slightly less than the expansion of the filament. By this means, the filament is relieved from tension, but has a negligible amount of slack in it, at its operating temperature.

The wire 14 being quite stifi, it does not vibrate at its free end to a troublesome degree, and the outer end of filament 19 is therefore held in place with a minimum possibility of vibration. The elasticity of the supports being confined to the wire 12, which is placed quite near the supporting press 3, the opportunity for vibration of the filament is reduced to a minimum.

The filament being under no tension, it has no tendency to continue in vibration when movement is communicated to it from its supports and container, which occurs when the container is struck or jarred. It may move slightly under the influence of an impact upon the device as a whole, but will not continue in vibrational movement. By this means the fluctuations in the current through the device, which are produced when a filament is stretched and allowed to vibrate, and which are perceived in connected telephonic apparatus as a very objectionable ringing sound, are prevented.

By this means, I have roduced a thermionic discharge device w 'ch is much less affected by impact and vibration than those constructed according to the prior art.

I have described a construction in which the axis of the reentrant portion of the container and the filament are parallel. My invention, however, is not limited. to such construction.

The structure described may instead be mounted in any desired position with respect to the axis of the reentrant portion or the axis of the container.

There is, as is well known, a best operating temperature for hot-cathode filaments; it is quite exactly fixed by the fact that, if heated higher, the filaments rapidly deteriorate and soon break, and, if operated cooler, their electron emission is greatly reduced. Where, in the following claims, it is stated that the cathode is heated, this should be understood to mean that it is heated to substantially this best operating temperature.

While I have shown only one embodiment of my invention in the accompanying drawing, it is capable of various changes and modifications without departing from the spirit thereof, and it is desired, therefore, that only such limitations shall be imposed thereon as are found in the prior art or are indicated in the appended claims.

I claim as my invention:

1. In combination, a press, a filamentary cathode and a pair of supporting wires sealed into said press, one of said wires being relatively stifi and the other of said wires being relatively flexible and curved to accentuate its springiness, said filamentary cathode being attached to ,said wires under a slight tension when cold and said flexible wire being adapted to take up only part of the expansion of said filament upon heating to an operative temperature.

2. In combination, a filament and a partially elastic support therefor adapted to maintain tension upon said filament when said filament is cold, to relieve tension upon said filament when it is hot and to compensate partially for the expansion of said filament upon heating.

3. In combination, a filament and a partially elastic support therefor adapted to take up a portion only of the expansion of said filament on heating.

4. A non-microphonic thermionic discharge device, comprising an evacuated container having a reentrant portion and a press thereon, an anode, a cathode, and mounting meansforsaid anode and said cathodecomprising a pluralit of wires sealed through said press, said cat ode comprising a filament attached to two of said wires, one of said wires being relatively rigid, the other being elastic, said filament being under a slight tension when cold, and the elasticity of. said mounting means being sufiicient to accommodate part only of the expansion of said filament on heating to operative temperature.

5. A thermionic discharge device, comprising a container having a reentrant portion, a press, a plurality of supporting conductors sealed therein, and a plurality of electrodes attached thereto, one of said electrodes being a filamentary cathode having one of its ends adjacent to said press and its longest dimension positioned in a direotion'extending away from said press, thereby causing its other end to be more remote from said press than its first-mentioned end, one of said supporting conductors being a substantially rigid wire and supporting said remote end of said filamentary cathode, a second of said supporting conductors being a less rigid wire that is bent to increase its elasticity and is positioned to support said adjacent end of said cathode, said cathode being attached to said supporting conductors under a slight tension when cold, and the elasticity of said second conductor being such as to take up a portion only of the expansion of said filament on heating.

6, The method of reducing microphonie noise in a thermionic triode device which eonsists in placing the filament under strain when cold and taking up only part of the expansion of the filament on heating, thereby causing it to be loosely supported at operating temperature.

7. In combination, a filament and a support therefor, said support being held in a strained position by said filament when cold 10 and permitted by the expansion of said filament to move to its unstrained position, the expansion of said filament upon heating to the operating temperature being more than sufficient to permit said movement.

In testimony whereof, I have hereunto subscribed my name this24th day of March, 1924.

HUBERT M. FREEMAN. 

